In a UMTS (Universal Mobile Telecommunications System) network, attempts are made to optimize features of the system, which are based on W-CDMA (Wideband Code Division Multiple Access), by adopting HSDPA (High Speed Downlink Packet Access) and HSUPA (High Speed Uplink Packet Access), for the purposes of improving spectral efficiency and improving the data rates. With this UMTS network, long-term evolution (LTE) is under study for the purposes of further increasing high-speed data rates, providing low delay, and so on (non-patent literature 1).
In the third-generation system, it is possible to achieve a transmission rate of maximum approximately 2 Mbps on the downlink by using a fixed band of approximately 5 MHz. Meanwhile, in a system of the LTE scheme, it is possible to achieve a transmission rate of about maximum 300 Mbps on the downlink and about 75 Mbps on the uplink by using a variable band which ranges from 1.4 MHz to 20 MHz. Furthermore, with the UMTS network, successor systems of LTE are also under study for the purpose of achieving further broadbandization and higher speed (for example, “LTE-advanced” (LTE-A)). For example, in LTE-A, there is a plan to expand the maximum system band for LTE specifications, which is 20 MHz, to approximately 100 MHz.
In LTE-A, uplink reference signals are enhanced, and the DM-RS (Demodulation-Reference Signal), which is used in channel estimation upon demodulation of the PUSCH (Physical Uplink Shard Channel) signal, the PUCCH (Physical Uplink Control Channel) signal and so on, is defined. This DM-RS is time-multiplexed and transmitted with the RBs (Resource Blocks) to transmit the PUSCH signal/PUCCH signal. For example, in the PUSCH, the DM-RS is multiplexed over the third SC-FDMA (Single Carrier Frequency Division Multiple Access) symbol in each slot.
Furthermore, in the LTE-A system, intra-cell orthogonalization is made possible by orthogonal multiple access on both the uplink and the downlink. That is to say, on the downlink, orthogonality is established between mobile terminal apparatuses, UEs (User Equipments), in the frequency domain. On the other hand, between cells, like in W-CDMA, interference randomization by one-cell frequency reuse is fundamental. So, in the 3GPP (3rd Generation Partnership Project), the coordinated multiple-point transmission/reception (CoMP) technique is under study as a technique for realizing inter-cell orthogonalization. In this CoMP transmission/reception, a plurality of cells coordinate and perform signal processing for transmission and reception for one user terminal UE or for a plurality of mobile terminal apparatus UEs. For example, for the downlink, simultaneous transmission of a plurality of cells adopting precoding, and coordinated scheduling/beam forming, are under study. By adopting these CoMP transmission/reception techniques, improvement of throughput performance is expected, especially with respect to user terminal UEs located on cell edges.